From owner-freebsd-fs@FreeBSD.ORG Thu Jan 27 01:42:51 2005 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1E6A516A4CE for ; Thu, 27 Jan 2005 01:42:51 +0000 (GMT) Received: from web41204.mail.yahoo.com (web41204.mail.yahoo.com [66.218.93.37]) by mx1.FreeBSD.org (Postfix) with SMTP id CE1DA43D46 for ; Thu, 27 Jan 2005 01:42:50 +0000 (GMT) (envelope-from arne_woerner@yahoo.com) Received: (qmail 57724 invoked by uid 60001); 27 Jan 2005 01:42:50 -0000 Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; b=rEDoahc+PPb6jHrc1jSCZis553HBB78rkP6gmUWO5Od0GEzRrMQNh40bquLLM0eP4Mwp4NPIRSJSY8kL8Q232wZA+Pcq1X/jSbxeJe2FUKcsSnZc5/oB/ImujcPCA5e6TrWcLcGrSUwSaoWiGEzuxB9ZyX+XziPBrpc7SWy7SeQ= ; Message-ID: <20050127014250.57722.qmail@web41204.mail.yahoo.com> Received: from [213.54.140.239] by web41204.mail.yahoo.com via HTTP; Wed, 26 Jan 2005 17:42:50 PST Date: Wed, 26 Jan 2005 17:42:50 -0800 (PST) From: Arne "Wörner" To: David Schultz In-Reply-To: <20050127004013.GA62561@VARK.MIT.EDU> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii cc: freebsd-fs@FreeBSD.ORG Subject: Re: ufs+softupdates / consistency X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 27 Jan 2005 01:42:51 -0000 --- David Schultz wrote: > On Wed, Jan 26, 2005, Arne WXrner wrote: > > > > The disc write cache could do that, but I disabled it in > > > > order to decrease the probability of inconsistency. > > > > > > Hopefully you disabled it on both FreeBSD and Linux, so > > > you're comparing apples to apples... > > > > > During the tests I enabled write cache in both settings, > > because I did not know how to turn it off in KNOPPIX... > > > > Isn't it possible to simulate the hard disc write cache in > > kernel? > > The write caching will make a big difference. Sorry, but I > don't know how to turn it off under Linux. Perhaps you could > turn it on under FreeBSD for the purpose of your performance > analysis. > Yes, I did. I enabled it in both test settings (KNOPPIX and FreeBSD). But I set hw.ata.wc to 0 in my every day setting. I just tried "dd of=a if=/dev/zero bs=32k count=1000" on a file system with hard disc write cache enabled and disabled and I saw no difference (appr. 5 Mbyte/sec, which is about 5 times less than a read from that file after the kernel cache was clear by other reads). Can somebody explain me, why hw.ata.wc does not change write speed? I would prefer hw.ata.wc=0, because it would be part of a damage avoidance system (I do not use an UPS and I have some write accesses over quite long periods of time caused by my TV cards (sys/dev/bktr)). Can somebody explain me, why write speed is so much slower than read speed (even with hard disc write cache)? I tried an UFS1 file system mounted async for another test. And the write speed was still about 5 Mbyte/sec. Can somebody explain me, what async filesystem I/O is (somehow my english is not sufficient to find that out)? -Arne __________________________________ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo